Vibrator and method of treating concrete



Sept. 15, 1936. w. H. HoRscH VIBRATOR AND METHOD OF TREATING CONCRETE Filed Oct. 29, 1931 4 Sheets-Sheer?l 1 jb. Z /j l NI hum; l

Sept. 15, 1936. w, H. HoRscH yVIBRATOR AND METHOD OF TREA'IINGl CONCRETE Filed Oct. 29, 1931 4 Sheets-Sheet 2 7 @24j M i j .M f @fm1 Sept. l5, 1936. w. H. HoRscH VIBRATOR AND METHOD OF TREATING CONCRETE Filed Oct. 29, 1931 4 Sheets-Sheet 5 Sept. 15, 1936. w. H. HoRscH 2,054,253"

VIBRATOR ND METHOD OF TREATING CONCRETE Filed. oct. 29, 1931 4 sheets-sheet 4 d n il.' A

Patented Sept. 15, 1936 UNITED STATES vmas'roa mcomf'rnon or marmo- BETE walter n. mmh, Wheaton, nl., minor te. Massey Concrete Products Corporation; Chi- `cago, Ill., a corporation of Virginia Application October 29,

193,1, semi N0. msu

The present invention relates to vibrators and methods of treating concrete, and is particularly concerned with apparatus and methods for high frequency vibration of concrete. The vlbrators themselves are. however, capable of general application and may be used in many different industries for producing mechanical vibrations, and I do not wish to be limited to the particular use described.

Vibrators employing an eccentric weight on the shaft of a. rotating motor amature, have been employed for mechanical vibration of concrete, and ordinary motors have been equipped with a small eccentric weight for the purpose of inducing some sort of movement due to the inertia and eccentricity of the weight. Ordinary motors are not provided with bearings adapted to withstand the strain which is put upon them when an eccentric weight is added to the shaft, and the use ofthe eccentric weight in the devices of the prior art has placed such a strain on the bearings that the life of the motor is very short. Furthermore, the single eccentric weight utilized on the motors of the prior art does not give vibrations in any predetermined direction, and it is very diiiicult to control the vibrations or movement induced by a motor having a single eccentric weight.

When a motor shaft is provided with a single eccentric weight at one end, and the shaft is rotated, the eccentric weight would be moved in a circle by the motor shaft were it not for the factthat the eccentric weight possesses inertia, and being subjected to a constant acceleration to maintain a circular path, the movement of the eccentric weight depends upon the amount of its mass relative to the mass of the motor and other parts connected tothe motor.

When a particle revolves in a circle, it has an acceleration toward the center which is equal to the square of the velocity divided by the radius.' and to cause this acceleration, there must be a force directed toward the center, and this centrifugal force may be determined according to the following equation:

F= mi,

where m represents the mass. Against this force the particle will exert an equal and opposite reaction on the body that exerts the force toward the center, that is, on that part of the weight which attaches the mass to the shaft, and through the shaft on the motor, and everything which is secured toit. Thus, the motor and its associatedmasses are endeavoring to` move the eccentric weight and the eccentric weight is reacting against the motor mass to move the motor. 'I'he result is that the eccentric weight moves in a smaller circular orbit than it would take if the vmotor could be assumed to be absolutely fixed, and the motor itself is oscillated in a relatively small circular orbit, the oscillation of the motor being opposite in direction to that of the eccentric weight.

'The sizes of these orbits depend upon the relative masses of the motor and eccentric v/eight and the square of the velocity of both masses. This can readily be demonstrated by 'referring to the i'ollewing equations in which the sub-indicia M is used for the motor, and the sub-indicia W for the eccentric weight. The centripetal force exerted on the eccentric weight by the motor to cause an acceleration toward the center and keep-the eccentric weight moving, may be expressed by the equation.-

Fm: mm rm The centrifugal force exerted'by the reac ien of the eccentric weight on the shaft may be expressed by the following equation:

n F, mw.;-

These forces must be equal and opposite, and it will thus be found that the relation of the masses velocities and radii of any particles subjected to these forces may be determined by the following equations:

prior art which are provided with small eccentric weights are fixedly secured to relatively stiff forms, such as cylindrical pipe forms, practically no vibratory enect is produced, because the weight of the concrete and pipe is added to the f the ordinary motors of the prior art were denitely limited-in the power of yvibrations which could be applied by reason of the definite limitation in the size of eccentric weights which could be` applied to the motor shaft, and the movement of the ordinary eccentric weight motors of the prior art could not be definitely controlled in direction for the reason that the motor tended to wobble in an orbit. f

This wobbling motion is further accentuated byl the fact that the eccentric weight was only placed on one endof the shaft, and the weight was not only eccentrically located with respect to the center of the shaft, but eccentrically located with respect to the center of mass of the motor.

Thus, the devices of the prior art tended to produce rotary oscillations rather than reciprocatory vibrations, and any reciprocatory vibrations that were secured were the result of the greater freedom of movement of the form or motor body in Vsome particular direction.

One of the objects of the present invention is the provision of an improved motor vibrator which is adapted to produce reciprocatory vibrations in a predetermined direction rather than rotary oscillations of the type' produced by the devices of the prior art.

Another object is the provision of an improved vibrator which is adapted to give longer and more efficient service by virtue of the fact that the motor bearings are not subjected to the constant wobbling motion of the motor and shaft which is present in the devic of the prior art, and also the provision of improved structures in which the vibrator itself may be provided with special bearings for withstanding any vibration-to which they are subjected.

Another object is the provision of an improved vibrator which is adapted to permit the use of more power inthe vibration of concrete or other articles, and which is adapted to exert greater force on the articles to be vibrated.

Another object is the provision of an improved vibrator, the effect of whichmay be controlled more readily, and the provision of improved vibrating apparatus by means of which the vibration of a multiplicity of different vibrators may be synchronized and maintained in :the proper direction, so that the different vibrators augment each otherseect rather than work against each other.

Another object is the provision of an improvedl method of manufacturing and treating concrete by means of which concrete of better characteristics may be made.

Other objects and advantages of the invention ywill be apparent from the following description,

and from the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.r

Referring to the drawings, of which there are four sheets;

Fig. l., is an elevational view inpartial section.

showing one form of vibrator constructed accord' ing to the present invention in connection with a supporting truck and a concrete form carried by the truck;

Fig. 2 is an elevational view in partial section,

showing the construction of the vibrating unit of Fig. 1; h

Fig. 3 is a transverse, sectional view taken on the plane of the line 3-3 of Fig. 2, showing the drive for the vibrating unit of Fig. 2;

Fig. 4 is an elevational view in partial section of another vibrator employing a direct drive;

Fig. 5 is a top plan view of the vibrator of Fig. 4, with the concrete form in section;

Fig'. 6 is an elevational or plan view of a. multiple vibrator installation. This figure represents an elevational view when the vibrators are applied to the bottom ofthe form for the purpose of effecting vertical vibration or a plan view when the vibrators are applied to the side of the form;

Fig. 7 is an elevational view in partial section, showing another vibrator adapted to produce controlled vibrations in a predetermined direction;

Fig. 8 is a sectional view of Fig. 7, taken on the plane of the line 3 3;

Fig. 9'is a sectional view similar to Fig. 8, of a modified form of gearing or drive for producing a higher rate of vibration.

Referring to Fig. 1,'this is an installation including a vibrator which may be used with any type of ordinary motor, for the reason that the motor itself is not subjected to the' vibration and its bearings are not subjected to any strains for which they were not designed. Thus, the

` installation 'of Fig. 1 includes anordinary motor 20, a flexible shaft 2i, and a vibrating unit 22 which may be iixedly secured to the truck 23. The truckl 23 supports one or more concrete forms 24 which are to be subjected to high frequency vibration in order to improve the characteristics of the concrete located in the forms 24, and the particular characteristics of the concrete andmixtures will be described in detail hereinafter.

The truck 23 may consist of a sheet metal truck having a platform 25 with a handle 26 and a plurality of wheel supports 21 secured to the platform 25 by riveting or spot welding at 28 and by braces 23. I'he wheel supports 21 may be provided with bores forming bearings for the wheel shafts30, but the shafts 30 are preferably `journaled in a movable bearing block 3l of substantially H-shape in cross section, which is slidably mounted in a slot 32 and urged downward by a compression spring 33. The bearing block 3| is retained in its slot by a plate 34 suitably secured by screw bolts on the wheel supports 21.

Where the wheels are secured to the truck without springs, vibration may nevertheless be effected, but the weight of the wheels is added to the weight of the truck, whereas the spring mounted wheels permit the vibration of the truck platform 25 and concrete forms without track 35 :and the form is resiliently supported on thespring 33.for vibration in a vertical directionl 'I'he vibrating unit 22 may consist of a casing 36 of -cast metal provided with attaching flanges y 31 which may be secured directly to the platform 25 by a plurality of screw bolts 33.

Referring to Fig. 2; the casing 38 may consist of a metal casting having substantially rectan4 guiar walls and provided with an open side ll which is covered by a cover plate 40. The cover plate may be secured to casing i5 by screw bolts 4| passing through the cover plate and threaded into the wall of the casting.

'I'he casing 38 is also provided with transverse circular bores 42, 4l aligned with each other and adapted to receive the bearings 44, 45 for the vibrator shaft 45. Bearing 45 may be secured in casing 26 by screw bolts 41 while the opposite bearing 44 may be secured inplace by the end fitting 48 of the flexible shaft 2i which is provided with casing 48.

The bearings 44, 45 may be made of special bearing metal and of any suitable size, weight and characteristics for withstanding the vibration to which the vibrator 22 is subjected, whereas the motor 25 which is connected to the vibrator by flexible shaft 2|. is not subjected to any unusual strains.

The shaft 45 is fixedly secured to a rotating gear or wheel 50 by means of a key 5I lin slot 52 and the shaft 45 is preferably provided with thrust bearings 53 on each side of the gear 55. The gear 50 may comprise a cast metal member which is formed with a hub 54, a web 55, and a rim 55 having teeth 51. One sector of the ,circular web 55 is preferably made thicker than the web 55, being substantially as thick as the length of the hub 54, forming an eccentric weight 58 on the gear 50.

'Ihe vibrator 22 is also provided with bearings similar to those described and shown in Fig'. 3, for the shaft 59 which is flxedly secured in the same way to a second gear or rotating member 50 having an eccentric weight 5I. All of the other details of shaft 59 and rotating member 50 may be exactly as described with respect to the details of Fig. 3, except that rotating member 50 is driven through the engagement of its teeth 51 with the teeth 51 of the gear 50, and therefore it need not be provided with a flexible shaft 2l.

'I'he teeth 51 of the gears |50 and B0 are so meshed with respect to the eccentric weights 58, 5I, that both weights are at the same side as shown in Fig. 2 when the weights are in that position, and when the gears rotate to theopposlte position both weights are at the opposite side of the vibrator. When the gear 50 is rotated in a clockwise direction it will be observed that both weights are adjacent each other between the shafts 45, 59 and whenl gear 50 has been rotated three-fourths of a revolution in a clockwise direction, both eccentric weights 55, 5I will be located at the opposite ends of the vibrator casing 35.

The casing may also be provided with laterally and rearwardly or downwardlyproiecting hooks 52 at each side for use in attaching the casing to articles to be vibrated by means of cables or other securing devices. When the vibrator is to be attached to a flat surface, the engaging surface 53 may be substantially plane. but when it is to be attached to a curved form, it may be curved complementarily to the form, such as a pipe form, or provided with an extra fitting to adapt it to the form, or with a pair of angularly disposed surfaces 54, 55, as shown in Fig. 5, for engaging circular forms of different size.

The mode of operation of the vibrator ol Figs. l` to 3 is as follows:

When the motor 2li is driven at an appropriate speed, such as, for instance, 3600 R. P. M., the gear 50 is rotated by means of flexible shaft 2| and gear 55 is rotated in unison with the gear 5l. When` the eccentric weights 5I, 5I are rotatins. and weight 55 is movlngin the direction of the arrow 55, the weight 5i is moving in the direction of the arrow 51. The weights` 5B and 5| are preferably equal in mass and consequently the force which would be exerted on the vibrator by weight 55 is counter-balanced by the force oi' weight '5| during this period of the rotation. It will be found that a similar situation exists whenI weights 5| and' 55 are moving in the direction of thearrows 55. 55 at the bottom of Fig. 2. The forces exerted on the vibrator by these eccentric weights are at all times equal and opposite to each .other in a horizontal direction in Fig. 2, and consequently there is no tendency to vibrate in the horizontal direction in Fig. 2.

When the weight 55 is moving upward in the direction of arrow 1li, weight 5i is moving upward in the direction of the arrow 1I, and the reaction causes an equal and opposite downward force indicated by the arrow 12 on the vibrator 22. When the eccentric weights are moving downward in the direction of the arrows 13 and 14, an equal and opposite upward reaction is produced on the .vibrator 22 in the direction of the arrow 15.

It will thus be observed that the present vibrator is adapted to eii'ect vibrations in a predetermined directlon, and the tendency to cause rotary oscillation or motion in any other direction is balanced out by the equal and opposite eccentric weights rotating in opposite directions.

In the present embodiment, the vibrator has been connected to the truck in such manner as to produce vertical vibrations for the purpose of causing the concrete mixture to settle into every portion of the form and to improve the characteristics of the concrete by the eliminationof air and excess water, and' by bringing the portions of the aggregate into closer engagement with each other, but the present vibrator may be utilized for inducing horizontal vibrations or vibrations in any predeterminedv direction, depending upon the mode of its connection to the form, concrete or vibrating members embedded in the concrete. y

It will thus be observed. that the direction of the vibrations may be controlled and their amplitude may be controlled since it is possible to use eccentric weights disposed at a greater radius. Ihe force of the vibrations may be controlled since it is possible to use larger masses `for eccentric weights in a vibrating unit particularly adapted to withstand such strains, and the speed of vibrations may be controlled by the interposition of a speed reduction or speed increasing gearing or a variable transmission 15 with or without a clutch 11.

Referring to Figs. 4 and 5, this is a modification comprising a vibrator unit 18 which is provided with a fitting 'is having the angularly disposed surfaces 54, 45 for. engaging the outside of a metallic pipe form 80. The vibrator may be secured on the pipe form by a plurality of cables 5I passing about the pipe form lll and having turnbuckles 82 engaging the hooks 52. It should be understood, however, that any of the forms or modes of securing the vibrator to the form may be employed, which are shown in my co-pending application, Case 2. Serial Numf ber 593,585, filed February 17, 1932, disclosing electromagnetic securing devices which may be attached to the concrete form by merely turning on the switch when the vibrator is in close juxtaposition to vthe form, thereby eliminating much of the labor in securing the vibrator to the form, and effecting a great saving of time when' a large number of different forms are vibrated.

The vibrating unit 10 is provided' with a base plate 00 having an upwardly projecting wail 04 which joins two casings 00, 00, similar in form to the casing 02 of the vibrating unit 22 previously described. The casing 00 comprises a pair of walls 81, 08 forming a. gear chamber 0l' for receiving the gears 00, 0| which are provided with eccentric weights 00, Blf similar to the weights of Fig. 2.

In this embodiment, the gears are iixedly secured to the shafts 02, 03 by set screws 00 and anti-friction roller bearings 95 havebeen provided with races 00, 01, cover plates 00, and oil seals 09. The motor |00 may have its base |0| bolted or otherwise secured to the base 00 and the motor |00 preferably has its shaft |02 substantially aligned with the shafts 03, |03 in the opposite vibrating units 0l, 00. The shaft |00 bears a similar eccentric weight gear |04 and a shaft |08 bears a similar eccentric weight gear |00. 'Ihe relation of the eccentric weight gears |04, |06 to each other is similar to the gears B0, 60, previously describedfand the weights are also so located that they bear a definite relation with respect to the weights on the gears 00, 0|

' at the other side of the vibrator, so that the 'eccentric weight on `gear |00 rotates in the same direction as the eccentric weight4 on gear 00 at the same time, and the eccentric weight on gear |04 rotates in the same direction as the eccenftric weight or gear 0| at the same time.

'Ihe motor shaft |02 is preferably connected to the gear shafts 90, |00 at each end through a universal joint |01 to eliminate the absolute necessity for perfect alignment between the motor shaft and the gear shafts. The universal joint |01 may vconsist of a pair of plates |00, |00 having apertures for receiving laterally projecting lugs ||0 on a fabricoid disc The operation of this vibrator is substantially as follows: When the eccentric weights are moving in a vertical direction in Fig. 4, the forces in# duced are counter-balanced, but when they are moving in a horizontal direction, the ,forces induced by the eccentric weights are additive and direct mechanical vibrations are produced in a horizontal plane. The provision of a separate vibrating unit 05, 00 'on each side of the motor, produces a balanced condition with respect to the motor, and there is less tendency for wobbllng of the motor shaft in a horizontal plane than would be the case if a single vibrating unit were employed..

structure or the stock of vibrator parts except the eccentric weight gears. l

The present vibrator is capable of producing vibrations in any predetermined direction, the vibrations being controlled and balanced with respect to the motorl structure, and while the 'motor is subjected to vibration with the unit, much wear on the motor may be eliminated. If desired, the motor may be supported on resilient rubber blocks interposed between the motor base and the vibrator base 0l to reduce the vibration on the motor.

The vibrations produced bythe vibrator in lconcrete for the purpose of improving its char- -to cause the concrete to slosh or move as a body back and forth in the form, separating from the wall of the form.

' Consequently, it is not desirable toexert too much power on any predetermined part of the form, and if the form or mass of the concrete cannot be placed in vibration by a single vibrator of reasonable size at one point, it is found desirable to utilize a plurality of vibrators llocated at regularly spaced points, or such points that the entire mass oi' concrete is placed in a proper state of vibration. l

'I'he vibrations spread -in all directions through the concrete from the point of their application, and they diminish in intensity and amplitude as `the distance increases from the source of vibrations, this decrease in intensity and amplitude being caused by the dissipation of the energy in the concrete and the frictional resistance which the particles have to movement of any kind.

Referring to Fig. 6, this is an elevational view with the form in section, showing a multiplicity of different vibrators adapted to synchronize to produce synchronized vibrations in various parts of the concrete H3, which is supported in form lil. If two vibrators are employed on the same mass of concrete, the vibrators working against each other, such as, for example, when one vibrator tends to' push in one direction at the same time that another vibrator tends to pushin another direction, the resultant vibration might be exactly zero if it were possible `to make the lforces kof the vibrators exactly equal and opposite. It

is a physical impossibility to cause -two electric motors of the oommutator type or induction type, or any other type except synchronous motors, to

rotate together, for the reason thatthere. is a .art are not synchronized and do not have their forces acting in the. proper direction at the proper vward. impulse on the form ||4, the eccentric weights of the units H0, ||1 also exert an upward impulse and the same action takes place when the units are exerting a downward impulse on the form.. As a result, all the vibrators vibrate together synchronously and the parts of the form adjacent to the vibrators, vibrate synchronously and vibrations are applied to a multiplicity of different parts of the form in the same direction and at the same time, the impulses being synchronized.

For this purpose, .the vibrating unit has its shaft ||8 connected by a universal joint ||3 to a shaft |20 of the unit H0. which in turn is connected by a universal Joint |2| to the shaft |22 of the unit ||1. When these units are connected together, they are connected with their eccentric weights in the proper position, and all of the units may be driven from the same shaft ||3 or a multiplicity of units of the type shown in Fig. 4 may be substituted for the vibrating units I I0, ||1.

It is thus optional to utilize with the unit ||0 a motor large enough to drive a number of different vibrators, or a plurality of different vibrators, each having a motor, may be connected together by shafts and universal Joints. I

It should be understood that the exible shaft drive shown in Fig. 1 may be utilized with a multiplicity of units of the type shown in Figs. 1 and 2, and flexible shafts may be employed between different vibrators to keep them in proper synchronized relation to each other, but in general, it will be found better to employ ordinary shafts and gearing for the reason that a flexible shaft permits more torsional movement, and after a period of operation, it may be found that vibrators connected by a flexible shaft will be slightly out of synchronous relation.

The vibrations which are induced in the form by the master vibrator ||0,will, however, tend to draw the other vibrators ||0, |I1 into synchronism, and therefore flexible shafts may be substituted for the shafts |20, |22 when the units are located close enough together on the form to take advantage of this situation.

Another mode of maintaining-the units in synchronous operation comprises the marking of weights and the provision of synchronous motors for operation on alternating current with special coils for starting the motors and marking devices for indicating the position of the eccentric weight in the vibrator so that the user may note whether or not the weights are all moving in the same direction at the same time.

By shutting oi?! the current and permitting the synchronous motor to skip, or by using some braking device to cause the synchronous motor to skip weights can be brought into synchronisrn and all the vibrators can be made to work together. For this purpose, the eccentric weight itself may be exposed through a window in the housing.

Another mode is to provide a temporary connection between' the synchronous motors during the starting of the separate motors.

It should also be understood that while all the vibrators are shown on the same side of the form in Fig. 6, they might be disposed on opposite sides of the form and timed to vibrate in opposite directions so that their vibrating effect on the concrete would be additive.

Referring to Fig. "I, this is another modified form of vibrator having a casing |23 supported upon a base |24 which may be similar to any of the bases previous! described for attachment to temporarily, the

circular or fiat concrete forms, and the vibrator casing |23 may be secured to the end of the motor casing |20 by a plurality of screw bolts 23. The vibrator casing |23 is closed by cover plate |21 and rotatably supportsa pair of shafts |23, |20 bearing gears |30, |3| having eccentric weights |32, |33, similarto those previously described in Fig. 2.

The casing |23 is also provided with a self-aligning anti-friction thrust bearing |34 consisting of the outer race |30, balls |30 and the inner race |31 disposed in a socket |33. A similarv bearing |33 is located at the other end of the casing |23 for rotatably supporting the worm sleeve |40 which is provided with a worm |4| for engaging teeth on the worm gears |30, |3I. Sleeve |40 may be provided with annular shoulders |42, |43

for engaging the bearings |34, |39 and preventy ing axial movement of the sleeve and the sleeve is provided with a circular bore |44 for slidably receiving the shaft |40 of motor amature |46. The,` bearing |30 may be secured in place by a cover plate |41 having an oil seal |48 and the shaft |40 is preferably provided with a keyway |49 for receiving the key |00 which also engages in a keyway |0| in the sleeve |40. 'I'he keyway |0| allows a sliding action of the key |00.

'Ihe upper end of shaft |40 may be engaged by a ball-bearing |02 resting in a circular socket |03 and engaged by a' spring |04 which reacts against a threaded cap |00. 'I'he other end of the armature shaft |40 may be rotatably supported in an anti-friction bearing |08 of the same type which is engaged by spring |01 which reacts against a threaded cap |00. Bearing |08 is adapted to slide in socket |09, but it is maintained in the position shown' by the action of springs l|04, |01. The commutator |00 may be made of sillcient length to maintain the commutator in contact with `the brushes I0 I, even though the armature may move backward and forward slightly againstl the pressure of springs |04, |01.

The operation of the present vibrator, is as follows. The eccentric weights |32, |33, are so arranged with respect to each other that vibrations are produced in a vertical direction in Fig. '1, or in the direction ofthe axis of the shaft |40. The motor shaft is thus arranged to extend in the direction of the vibrations and the motor shaft is resiliently supported so Athat although the vibrator and motor casing |20, and the motor field are vibrated with the form, these vibrations do not exert any particular strain upon the bearings of practically assume a position of rest in an axial direction, and the shaft |40 may slide backward and forward in the sleeve |40 or rather, the sleeve may slide backward and forward on the shaft as the vibrator casing moves back and forth.

Shaft |40 slidably engages worm sleeve! |40, but causes the worm sleeve to rotate and driver'the gears |30, |3| in opposite directions in afmanner similar to the vibrator of Fig. 2, but the motor shaft is not subjected to the lateral forces which tend to damage the motor bearings and the vibration merely results in relative sliding movement between the motor shaft and its bearings, which is resisted by the springs |04, |01;

the motor, because the armature |40 may Referring to Fig. 8, this islel fragmentary, de-

|30 is provided with the lining of bearing metal |65.

Referring to Fig. 9, it will be observed that the direct worm drive may be replaced by a worm drive through the gears |66 and pinions |61, thereby permitting the eccentric weight |32, |33 to be driven at a greater speed, and the speed of vibration is not necessarily limited to that which can be attained by the worm drive shown in Fig. '7, since it will be observed that smaller pinions may be used-on shafts |28, |29, and the worm |4| need not necessarily directly engage teeth on the eccentric weight gear. A

The present vibrators may be used with electric motors and gearing to produce vibrations having frequency of several thousand vibrations per minute, or less, up to 3600 vibrations per minute, which is a very common motor speed, or

the vibrations may be increased by the use of a faster motor or speed increasing gearing to any number of vibrations per minute, which the strength of the rotating parts permits. A practical limit is that at which the fastest rotating parts may safely be rotated, this speed of rotation being limited by the centrifugal force, and the present vibrators are capable of attaining vibrations of sufficiently high frequency to produce very beneficial results in the treatment of concrete.

The concrete which is utilized in the forms 24 or H4, may consist of a mixture of water, Portland cement, and aggregate consisting of relatively small pieces of stone, such as marble or granite, and the mixture maybe sumciently dry so that there is practically no slump in the concrete as it is placed in a form, or upon any other support. Such a mixture may be described as dry or nonworkable on account of the lack of any tendency to flow into the parts of any form, and vibrators of the type illustrated may be used for vibrating the greenconcrete at a high frequency to cause the aggregate to fill every part of the form, remove air voids and excess water, and improve the granular structure and strength of the concrete.

After such concrete has been subjected to vibration during the placing of the concrete, and in many cases for a short time after the concrete has been placed, the form and molded concrete member may be subjected to a wet steam bath. After this curing, the external surface of the molded /concrete member is dried, ground and polished,

and the concrete members so manufactured present the appearance of native granite or marble, or any of the other types of stone, depending upon the kind of aggregate used.

The concrete members may be made in any shape, with a minimum amount of stone work, since the concrete members may be molded as desired and a very high strength may be attained by the use of high frequency vibration for treating concrete of this kind.

High frequency vibration is preferably employed with semi-wet mixtures for producing concrete of very desirable characteristics for ordinary concrete work, and in any event, sunlcient vvate` v should be provided to hydrate all of the cement.

It will thus be observed that I have invented an improved vibrator which is adapted to produce vibrations in a predetermined direction, and which is adapted to permit the better control of the vibrations with respect to direction.k amplitude, intensity and synchronization.

While I have illustrated a preferred'embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details oi' construction set forth, but desire to avail myself of all changes within the scope of the appended claims. Having thus described my invention, what I claim is new and desire to secure by Letters Patent of the United states, is: y f/ 1. Vibrator mechanism comprising Ia unitay member to be vibrated, a plurality of vibrator housings secured tosuch unitary member and each supporting a shaft with an eccentric weight secured thereto, said weights extending from their respective shafts in the same angular direction and said shafts being set in approximately tandem alignment with each other, flexible couplings connecting the shafts of the vibrators so that they will rotate in synchronism with each other and means for imparting rotative motion to said coupled shafts.

2. Vibrator mechanism comprising a unitary member to be vibrated.- a plurality of vibrator housings secured to such unitary member and each supporting a shaft with an eccentric weight secured thereto, said weights extending from their respective shafts in the same 'angular direction, in combination with a motor actuated driving shaft and flexible couplings connecting the shafts of the motor and vibrators in tandem so that all so connected shafts will rotate in angular unison.

3. A vibrator mechanism comprising a unitary member to be vibrated, a plurality of vibrators secured to said unitary member, each vibrator hav-I ing a shaft withl an eccentric weight secured thereto, said weights extending from their respectiveshafts in the same angular direction, and said shafts being set in approximately tandem arrangement 'with each other, flexible couplings connecting the shafts of the vibrators so that they will rotate in synchronism with each other, and means for imparting rotative motion to the coupled shafta, comprising an electric motor resiliently mounted with respect to said unitary member, and flexible driving means connecting said motorand one of the shafts of said vibrators.

4. A vibrator mechanism comprising a unitary member to be vibrated, a plurality of vibrators secured to said unitary member, each vibrator having a shaft with an eccentric weight secured thereto, said weights extending from their ree spective shafts in the same angular direction, and said shafts being set in approximately tandem arrangement with each other, flexible couplings connecting the shafts of the vibrators so that they win rotate in synchronismwith each 60 other, means for imparting 'rotative motion to the coupled shafts, comprising an electric motor resilientiy mounted with respect to said unitary member, and flexible driving, means connecting said motor and one of the shafts of said vibrators, said flexible driving means `comprising a flexible shaft extending from the motor shaft to the said latter vibrator shaft.

WAL'I'ER H. HoRscH. 70 

